It is becoming increasingly more evident that simulation cannot provide full verification for today's complex designs. Formal verification is emerging as an alternative technique to simulation that promises to guarantee complete verification. However, because of its inability to handle all classes and sizes of designs, this technology is also incomplete. The solution is to combine the two complementary techniques, using their respective strengths. The authors of this article have developed such a technique for hybrid verification. They illustrate its application through two case studies in protocol bridge verification. In both designs, the hybrid technique was able to discover bugs that simulation and formal verification had failed to find individually.